1. Field of Invention
This invention relates to a polyethylene terephthalate composition containing the sodium salt of a hydrocarbon acid and an aliphatic plasticizer.
2. Description of the Prior Art
It is known to use nucleating agents in crystallizable polymers such as linear saturated polyesters of aromatic dicarboxylic acids. U.S. Pat. Nos. 3,435,093, 3,516,957 and 3,639,527, as well as Dutch Pat. Nos. NL7901009 and NL7901605, disclose various approaches to molding thermoplastic compositions of linear saturated polyesters of aromatic dicarboxylic acids, and are particularly applicable to polyethylene terephthalate. These patents generally disclose the use of salts of hydrocarbon and polymeric carboxylic acids as nucleating agents for linear saturated polyesters. Other patents of interest relating to crystalline polyester compositions include: U.S. Pat. Nos. 3,516,957 and 3,435,093.
A molding formulation based on a linear saturated polyester, such as polyethylene terephthalate, should result in molded product having good physical properties including flexural strength, modulus, tensile strength and impact properties. Further, the molding compound should also have good molding properties including a melt flow index for sufficient flow into the mold, good mold release properties and good finished appearance.
From a practical point of view, it is desirable that satisfactory properties, as outlined above, be attained using water heated molds. That is, molds heated to temperatures between 76.degree. C. to 100.degree. C. In order to accomplish this, it is desirable for crystallization to begin at as high a temperature as possible upon the cooling of the polyester which was fed into the mold and continue during the cooling to as low a temperature as possible. T.sub.cc is a measurement to determine at what temperature crystals first appear upon cooling from the melt. T.sub.ch is a measurement which indicates the temperature at which crystallization is no longer occurring upon cooling. It has been found that mold appearance and mold release properties can be related to T.sub.ch. T.sub.ch is determined by measuring the temperature at which crystals first appear upon heating an amorphous piece of polyester. T.sub.cc and T.sub.ch can be measured using a Differential Scanning Calorimeter.